Problem: $ { {-4} \times \left[\begin{array}{rrr}{2} & {1} & {-1} \\ {1} & {4} & {-2}\end{array}\right] = {?} } $
To multiply a matrix by a number, multiply each item of the matrix by the number. ${\left[\begin{array}{rrr}{-4}\times{2} & {-4}\times{1} & {-4}\times{-1} \\ {-4}\times{1} & {-4}\times{4} & {-4}\times{-2}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{rrr}{-8} & {-4} & {4} \\ {-4} & {-16} & {8}\end{array}\right]}$